Microbiology Nuts & Bolts Test Yourself - Primary Care Begin here

The patient in this test yourself case is entirely fictitious, however it is based on many clinical scenarios the author has come in to contact with during his medical career. Any similarity to a real case is entirely coincidental.

Doris 86 year old nursing home resident Nursing home ask for a visit as she is becoming increasingly confused and has developed new urinary incontinence On examination she is afebrile but appears to have some suprapubic discomfort A Midstream urine is taken The urine dipstick is positive for leucocytes and nitrites

What is the correct interpretation of the urine dipstick result? Doris has a UTI Doris does not have a UTI A UTI cannot be excluded A UTI can be excluded A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: a UTI cannot be excluded A definition of infection is inflammation or tissue destruction in the presence of a microorganism Leucocytes are the white blood cells that indicate an inflammatory response The nitrites are bacterial nitrites, breakdown products produced by bacteria Leucocytes and nitrites in a urine sample mean a UTI is possible but there are other reasons why they might be there and so they do not prove a UTI, they just mean it cannot be ruled out The positive predictive value of a urine dipstick is 60% The negative predictive value of a urine dipstick is 97% A negative urine dipstick can exclude a UTI in most patients

Doris The MSU is sent to the microbiology laboratory in a red topped boric acid container Doris is started on Trimethoprim for a possible UTI as there is not other obvious focus of infection

Why is the MSU sent in boric acid? The lab analyser needs boric acid Boric acid prevents damage to the container The MSU should not be sent in boric acid Boric acid stops the urine sample degrading A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: the boric acid stops the urine sample degrading The boric acid stops the bacteria in the sample from growing and giving a false positive culture result Urine culture is a quantitative test; the lab reports the actual number of bacteria present in a millilitre of urine If the bacteria are allowed to grow in the time it takes for the sample to get to the laboratory then the number of bacteria within the urine will be falsely high and suggest the presence of a UTI even if the patient doesn’t actually have a UTI NOTE: the urine sample should not be taken directly into the boric acid container as the dipstick cannot be done on acidified urine, the urine should be transferred to a boric acid container for transport to the laboratory

Why do we take midstream urines? To get rid of non-sterile urethral urine Only the upper urinary tract can be infected To stop the container being over filled Microbiologists like to make life difficult! A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: to get rid of non-sterile urethral urine The normal bacterial causes of urinary tract infections come from the gastrointestinal tract These bacteria colonise the skin of the perineum and then swim up in to the urethra Voiding and discarding the first part of the urine stream gets rid of the bacteria in the urethral urine and reduces the risk of contamination giving a false positive culture result

Doris Doris initially started to improve but three days later she became short of breath and started coughing up thick green sputum On examination she had a temperature of 38.5 o C and was a bit tachycardic She was diagnosed with pneumonia

Which of the following is NOT a sign of pneumonia? Cough Fever Purulent sputum Crackles on auscultation A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: crackles on auscultation According to the British Thoracic Society the clinical diagnosis of pneumonia is: –Cough PLUS 1 lower respiratory tract symptoms PLUS new focal chest signs PLUS 1 systemic symptom –No other explanation –Lower respiratory tract symptoms include: shortness of breath, purulent sputum, chest pain –Focal chest signs include: reduced chest movement, dull percussion, bronchial breathing, increased tactile vocal fremitus or vocal resonance –Systemic symptoms include: fever, sweats, shivers, aches, pains Crackles in the chest usually indicate heart failure, fibrosis, chronic obstructive pulmonary disease or pneumonitis

Which of the following would be appropriate empirical antibiotic(s)? PO Amoxicillin PO Amoxicillin PLUS PO Clarithromycin PO Cefradine PO Clindamycin A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: PO Amoxicillin As long as Doris is not allergic to penicillin then PO Amoxicillin will cover the common causes of mild to moderate community acquired pneumonia (CAP) Alternatives in penicillin allergy are PO Clarithromycin or PO Doxycycline The most common causes of mild to moderate CAP are: –Streptococcus pneumoniae –Haemophilus influenzae –Viruses There is no need to use combination therapy Cefradine would work but is too broad spectrum and poses a high risk for Clostridium difficile associated disease (CDAD) Clindamycin does not cover the causes and is a risk for CDAD

Doris Doris is started on Amoxicillin and a sputum sample is taken and sent to the microbiology laboratory the next day Two days later Doris is feeling a bit better The sputum sample result is: –Appearance: salivary –Culture: Klebsiella pneumoniae isolated resistant to Amoxicillin, sensitive to Co-amoxiclav, Cefradine and Ciprofloxacin

What is the correct interpretation of the sputum result? K. pneumoniae is the cause of her CAP The lab has contaminated the sample K. pneumoniae is a colonising bacterium Doris probably has cancer A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: K. pneumoniae is a colonising bacteria All K. pneumoniae are resistant to Amoxicillin When patients are given antibiotics their normal flora changes due to the selective pressure of the antibiotic killing off normally sensitive bacteria In patients who are unwell gastrointestinal bacteria are able to colonise their upper respiratory tract replacing the normal sensitive bacteria In this case Doris was correctly given Amoxicillin and this has selected out the K. pneumoniae The main clue to this is the fact that the sputum sample is salivary indicating that it is not sputum but spit and therefore will contain bacteria from the mouth not the lungs

Doris Having been bed bound for a week with a UTI followed by pneumonia Doris develops a pressure sore on her sacrum This becomes increasingly painful and erythematous She is started on PO Flucloxacillin but 2 days later the infection appears to be worsening

What is the likely bacterial cause for the worsening infection? Pseudomonas aeruginosa Clostridium perfringens Group A Beta-haemolytic Streptococcus Meticillin-resistant Staphylococcus aureus A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Meticillin-resistant Staphylococcus aureus (MRSA) The most common causes of skin and soft tissue infections are Staphylococcus aureus and the Beta-haemolytic Streptococci Groups A, C & G The Beta-haemolytic Streptococci are unlikely in this situation because Doris has been on Amoxicillin and Flucloxacillin leading up to the development of cellulitis and both of these antibiotics are active against these bacteria The most likely cause is therefore a S. aureus resistant to Flucloxacillin i.e. MRSA Pseudomonas aeruginosa and Clostridium perfringens are not common causes of skin and soft tissue infections –Pseudomonas aeruginosa commonly colonisers the warm moist tissue of broken down areas of skin such as ulcers –Clostridium perfringens is normally associated with soft tissue infections following penetrating injuries

Doris While waiting for the results of swabs from the sacral sore to come back Doris was started on PO Clindamycin

What would have been a more appropriate choice of antibiotic? Erythromycin Doxycycline Teicoplanin Fucidic Acid A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Doxycycline Doxycycline is almost always active against MRSA in the UK and can be taken orally Clindamycin is not the best choice as it is unpredictable whether it will be active against MRSA and it is high risk for CDAD Erythromycin activity against MRSA is unpredictable Teicoplanin is active against MRSA but it is only available IV Fucidic Acid should never been used on it’s own either PO, IV or topically as resistance develops very quickly, even within 24 hours!

Doris Two days after starting the PO Clindamycin Doris develops severe diarrhoea She is admitted to hospital where she is diagnosed as having CDAD Despite appropriate treatment Doris sadly dies 2 days after being admitted to hospital

What was the cause of her CDAD? PO Clindamycin PO Flucloxacillin Multiple courses of antibiotics Clostridium difficile A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Clostridium difficile Antibiotics predispose to CDAD but they do not cause it CDAD is an infection caused by the bacterium Clostridium difficile – without the bacterium you don’t get CDAD The antibiotics predispose to CDAD because the bacterium is resistant to those antibiotics and is therefore left behind or allowed to colonise when the normal sensitive bacteria are killed off

Doris A root cause analysis is done on why Doris developed CDAD and whether any lessons should be learned to prevent future patients having the same problem The RCAs identified where: –Inappropriate antibiotic prescription of Clindamycin –Poor infection control practices in the nursing home

Which of the following are common root causes for CDAD? Poor hand hygiene Inappropriate choice of antibiotics Failure to isolate patients with diarrhoea Prolonged courses of antibiotics A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: all of the answers are correct The prevention of CDAD requires: A multifactorial infection control approach to manage the patients environment to reduce the risk of exposure to the bacterium Clostridium difficile Good antimicrobial stewardship to ensure the patient only ever receives the right antibiotic, at the right dose, route and duration, for the right infection at the right time All healthcare professionals have a responsibility to ensure this happens

Doris The GP and the nursing home were devastated by the findings of the root cause analysis, but they made sure they learned from their mistakes, and put policies and procedures in place to prevent this happening again. The End

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